In some types of known silent chains for transmitting power between rotating sprockets, first and second links, composed respectively of a plurality of first link plates and a plurality of second link plates, are arranged alternately along the length of the chain with their link plates interleaved and connected articulably by rocker-type connecting pins. Each of the connecting pins is composed of two rocker pins arranged to roll on each other. The connecting pins extend through aligned pin holes in the overlapping parts of the first and second link plates.
The first and second links bend relative to each other about axes approximately centered on the connecting pins. As the chain engages with and disengages from a sprocket, a periodic, so-called “polygonal” action takes place which can cause a phenomenon referred to as “string vibration,” i.e., vibration in a direction orthogonal both to the longitudinal direction of the chain and to the direction of the width of the chain. String vibration therefore takes place in the plane in which the chain bends as it travels around the sprockets with which it is in mesh. String vibration generates noise and causes abrasion between the rocker pins and the edges of the pin holes in the link plates, through which the rocker pins extend.
When the frequency of the polygonal action coincides with or approaches the natural resonance frequency of a free span of the chain, the magnitude of the string vibration increases causing increased noise and abrasion.
In order to suppress string vibration, attempts have been made to prevent adjacent links from being put into a backwardly bent condition, i.e., a condition in which one of two adjacent links bends outward relative to the other beyond a straight condition, in a direction opposite from the direction in which bending takes place when the links begin to engage a sprocket. Examples of such chains are described in United States patent publication 2003/0233821, U.S. Pat. No. 6,387,003, and laid-open Japanese Utility Model Application S62-196950.
In some of these chains, gaps are provided between the rocker pins and the bend blocking surfaces when the adjacent links are in the straight condition. When the gaps are small, they reduce string vibration to some extent compared to a case in which there is no bend-blocking surface. However, the gaps still allow string vibration at a significant amplitude, and allow noise to be generated by contact generated between the rocker pin and a bend-blocking surface when the amplitude of the string vibration increases.
In other such chains a bend-blocking surface is provided with a projection that blocks the adjacent links from bending backward by contacting a rocker pin. Here a concentration of stress occurs which can impair the durability of the link plates and therefore impair the overall durability of the chain.
Accordingly, there is a need for a chain that reduces noise and abrasion caused by string vibration, that reduces the noise caused by contact between the rocker pins and the edges of the pin holes that results from string vibration, and that improves the durability of the link plates and the overall durability of the chain.